In a working vehicle on which a slewing base is mounted, it is necessary to supply a working medium such as hydraulic oil, air, or hot water from a hydraulic power source, an air pressure source, or a hot water source disposed on the traveling vehicle, to each of a hydraulic device, a pneumatic device, and a heating device mounted on the slewing base. Such a working medium is adapted to be supplied to each device via a swivel joint because the slewing base slews on the vehicle frame.
A swivel joint of Patent Literature (hereinafter, abbreviated as PTL) 1 is for different kinds of fluid for supplying and discharging hydraulic oil, hot water, and air. As illustrated in FIG. 8, the swivel joint has a structure in which inner cylinder 121, intermediate cylinder 131, and outer cylinder 141 are fitted concentrically.
Upper portions of about ⅔ from the top in the height direction of outer cylinder 141 and intermediate cylinder 131 are allocated for a hydraulic oil passage. The hydraulic oil passage is mainly configured of a plurality of inner annular grooves 148 formed on the inner circumferential face of outer cylinder 141, and a plurality of intermediate cylinder side passages 132 perforated vertically in the wall body of intermediate cylinder 131.
Lower portions of about ⅓ from the bottom in the height direction of outer cylinder 141 and intermediate cylinder 131 are allocated for a hot water passage. The hot water passage is mainly configured of inner annular grooves 149 formed on the inner circumferential face of outer cylinder 141, and a plurality of intermediate cylinder side passages 133 perforated vertically in the wall body of intermediate cylinder 131.
A lower portion of intermediate cylinder 131 and inner cylinder 121 are allocated for an air passage. The air passage is mainly configured of a plurality of outer annular grooves 129 formed on the outer circumferential face of inner cylinder 121, and a plurality of intermediate side passages 134 perforated axially in the wall body of intermediate cylinder 131.
Adjacent to respective annular grooves 148, 149, and 129 in the upper and lower direction, annular packings 146, 147, and 127 are fitted.
In the aforementioned conventional technology, it is characterized that annular grooves are not processed on the inner circumferential face and the outer circumferential face of intermediate cylinder 131. This makes processing of intermediate cylinder 131 easy.
Further, the hot water passage portion located at about ⅓ from the bottom of intermediate cylinder 131 and outer cylinder 141 have smaller outer diameters compared with that of the hydraulic oil passage portion located above it, thereby improving the assemble property when intermediate cylinder 131 is assembled into outer cylinder 141.
However, the aforementioned conventional technology involves the following problem:
(1) While hot water is supplied to and discharged from inner annular grooves 149 of the hot water passage of outer cylinder 141, as the lubricating property of water is low, intermediate cylinder 131 is worn quickly, whereby the frequency of replacement of intermediate cylinder 131 increases. As intermediate cylinder 131 is a large member having a height dimension of about the same as that of outer cylinder 141, and is a member which is difficult to be processed and in which a plurality of passages must be perforated in the wall body, there is a problem that the replacement cost for intermediate cylinder 131 is high and the replacement work takes labor.